1. Field of the Invention
The present invention relates generally to the field of microstructure devices, and more particularly to a microstructure device incorporating a porous membrane.
While the present invention is subject to a wide range of applications, it is particularly well suited for extractor, separator, diffuser, and contactor applications in the field of microfluidic reactor systems.
2. Technical Background
Reactor systems incorporating porous membranes, known generally as membrane reactors, have typically been used to achieve separation of multi-phase complex feeds, or to filter a single phase. Generally speaking, the porous membrane within conventional membrane reactors may exhibit micro-to-macro porosity, and may be fabricated from a number of materials. Porous materials are commonly categorized according to their (average) pore size. Microporous materials generally have pore diameters less than or equal to 10 nanometers (nm), mesoporous materials typically have pores in the range of about 2.0 to 50.0 nm and macroporous materials typically contain pores as large as about 250 nm. See, IUPAC Manual of Symbols and Terminology, Appendix 2, Part 1, Colloid and Surface Chemistry, Pure Appl. Chem. 31, 578 (1972). Depending upon, among other factors, the average pore size, certain porous membranes may serve as a support structure for a catalytic material, if required by a particular application.
Porous membranes used in membrane reactors are now generally classified based on the role or function of the membrane in a given reactor. Conventionally, porous membranes within membrane reactors may be classified by one of three functions. If the function of the membrane is principally to selectively remove, from the reactor, a product of an equilibrium-restricted reaction, in order to gain yield on conventional reactors, or to remove one or several components within a complex mixture, the membrane reactor is typically classified as an, “extractor.” In other applications, the role of the membrane is to dose a reactant that may originate successive reactions. As the targeted product is often a product of primary addition, the regulation of this reactant concentration by permeation through the membrane may improve the selectivity. When compared to a conventional reactor, the same amounts of reactants may be introduced, but here, one of them is distributed by the membrane along a catalyst bed. This type of membrane reactor is thus typically termed a, “distributor” or a “diffuser.” The third type of membrane reactor generally takes advantage of the unique geometry of the membrane, e.g., a permeable wall separating two media. When the membrane is also a support for a catalyst, it is possible to feed the membrane from both sides with reactants (for instance gas from one side, liquid from the other) or to force a reactive mixture through the reactive wall. In the first case, it is possible to favour the contact between the catalyst and the reactant that is limiting the performance in conventional reactors (e.g., gas in gas-liquid-solid processes, hydrophobic reactant with hydrophilic catalyst, etc.). In the second case, the residence time in the active pore of reactants and products is controlled by operating parameters (pressure drop across the membrane) and not by diffusion. This may lead to better control of activity or selectivity. In the two cases, the role of the membrane is to favour contact between reactants and the catalyst. Such a membrane reactor is generally known as a “contactor.” More specifically, the first contactor mode described above being termed an “interfacial contactor,” and the second mode being termed a “flow-through contactor.”
Typical membrane reactors utilized in the art are constructed of concentric tubes (the membrane being the inner tube). One specific tube-type membrane reactor is known as a packed bed membrane reactor (PBMR). Such a membrane reactor combines a tubular porous ceramic membrane and a fixed bed catalyst placed in the core volume of the ceramic tube. The membrane reactor module is typically made of a stainless steel shell containing the composite membrane tube, which is packed with the catalyst. Generally speaking, the ends of the membrane tube are enameled and equipped with compression fittings such as graphite seals in order to ensure tightness between the inner (retentate or tube side) and the outer (permeate or shell side) compartments. In such a conventional tube-type membrane reactor, fluids are simply delivered to the reactor at one end of the tube, while the other end of the reactor serves as an outlet port. As one of skill in the art readily recognizes, industrialization and parallelization of such tube-type reactors is complicated and difficult to implement. Moreover, control of the reaction requires complex fluid management outside of the reactor, particularly upstream of the inlet port or ports. In addition to these shortcomings the structure of tube-type membrane reactors provides poor mechanical support for the catalyst material(s), and is not easily sealed. Accordingly, leakage from such devices is generally the norm, which significantly adversely effects efficiency.
With the advent of microreactor technology, attempts have recently been made to reduce the scale of membrane reactors, and thus minimize the sealing and leakage shortcomings discussed above. In connection with one microreactor approach, a porous membrane is supported about its periphery with a metal frame to form one of many laminate layers within the microreactor. The porous membrane is typically a micromachined metal layer, such as stainless steel or copper, but materials such as plastics and ceramics have been the subject of experimentation. The microlamination processing techniques and other techniques necessary to manufacture such porous layers is generally cost prohibitive for mass production, and porous membranes manufactured by these techniques have been found to have limited application for chemical processing.
What is needed therefore, but seemingly unavailable in the art, is a microstructure device incorporating a porous membrane and method of manufacturing such a microstructure device that overcomes shortcomings associated with membrane microreactors known in the art.